We present a new empirical charge model that describes atomic and molecular fragments as open, interacting quantum mechanical systems coupled together by a common reservoir of charge. Unlike existing fluctuating-charge models, this model naturally reproduces the noninteracting limit whereby the energy varies piecewise linearly with charge as required for the physical system. We present numerical results for donor-acceptor systems. First, we develop a model that reproduces both the ground and first excited singlet state surfaces of lithium fluoride using the same set of parameters. Second, we develop an empirical potential that can be fit accurately to both the neutral and monocation curves of benzene dimer simultaneously. Our new open fragment model provides a new way to develop minimally parameterized force fields that treats ground and excited electronic states equally, thus allowing for accurate descriptions of charge transfer excitations and ionization processes.

Quantum mechanical charge equilibration model for open fragments: Extending force fields to handle molecular excited states

244th National Meeting (2012)

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